應用基本控制點於地籍圖坐標轉換精度之研究

Accuracy of Coordinate Transformation Using Basic Control Points for Digitized Cadastral Map

台灣地區仍有許多地籍圖為圖解法測繪，達約900萬筆，地政單位近年來推動將圖解地籍圖數值化，將於94年全面辦竣。地籍圖數值化，除達到避免圖籍繼續伸縮破損之目的外，其數化成果更可提供各項地理資訊系統應用。圖資整合運用與否的關鍵在於能否同時表現，就空間資料而言是否在同一坐標系統就很重要。目前圖解數化成果管理系統提供將數化成果轉換為TWD67坐標之輸出功能，該轉換模式係基礎於以早期地籍三角點與虎子山TWD67系統共同點，以最小二乘共置法所解算台灣全區500Ｍ網格及雙線性內插法，精度約1-2M。內政部於87年公布TWD97坐標系統及一二等衛星控制點成果，土地測量局自84年起陸續布設三等控制點，亦已全面採用及改算TWD97成果，密度達平地2公里山地3-8公里一個點位。本研究選擇三個試驗區，以圖解法鑑界方式實地測定三等控制點之地籍坐標，據以求解該區域〔地籍坐標－－TWD97〕之坐標轉換參數，並以實地測量界址點，運用統計測試並檢核分析圖解數化地籍圖坐標轉換後之精度。 About 9 million parcels of cadastral maps were made using direct map conversions. Digitization of these maps is currently being carried out by land administration officials and will be completed in 2005. Digitization protects these maps from destruction and distortion, and also facilitates the use of GIS. The Digitized Cadastral Map Management System can export data in the TWD67 coordinate system. In this system, coordinate transformation to TWD67 is based on the result derived from co-located triangulation points and TWD67 control points, the latter having the origin at Mt. Hu-Tze. The transformation parameters are computed on a 500m×500m grid using the least squares collocation method. At any desired point, a bilinear interpolation from the grid is used to obtain transformation parameters. The accuracy of such a coordinate transformation is about 1- 2 m. The coordinates of the 1st- and the 2nd-order satellite control points in the TWD97 system were officially published by the Ministry of the Interior in 1998. The Land Survey Bureau has been establishing the 3rd-order control points since 1995. The coordinates of the 3rd-order control points are highly accurate and are spaced at a 2-km interval in the flat areas and at a 3-km to 8-km interval in the mountainous areas. In this study, three testing areas are chosen. In each area the coordinates of the 3rd-order control points are derived from a field coordinate-setout from the corresponding cadastral maps. Then, transformation parameters at the control points are derived and theirs coordinates in TWD97 are computed. The map-derived TWD97 coordinates of the control points are used to obtain coordinates of land boundaries, which are then compared with the GPS-measured coordinates. This comparison helps to assess the accuracy of coordinate transformation for the digitized maps.

About 9 million parcels of cadastral maps were made using direct map conversions. Digitization of these maps is currently being carried out by land administration officials and will be completed in 2005. Digitization protects these maps from destruction and distortion, and also facilitates the use of GIS. The Digitized Cadastral Map Management System can export data in the TWD67 coordinate system. In this system, coordinate transformation to TWD67 is based on the result derived from co-located triangulation points and TWD67 control points, the latter having the origin at Mt. Hu-Tze. The transformation parameters are computed on a 500m×500m grid using the least squares collocation method. At any desired point, a bilinear interpolation from the grid is used to obtain transformation parameters. The accuracy of such a coordinate transformation is about 1- 2 m. The coordinates of the 1st- and the 2nd-order satellite control points in the TWD97 system were officially published by the Ministry of the Interior in 1998. The Land Survey Bureau has been establishing the 3rd-order control points since 1995. The coordinates of the 3rd-order control points are highly accurate and are spaced at a 2-km interval in the flat areas and at a 3-km to 8-km interval in the mountainous areas. In this study, three testing areas are chosen. In each area the coordinates of the 3rd-order control points are derived from a field coordinate-setout from the corresponding cadastral maps. Then, transformation parameters at the control points are derived and theirs coordinates in TWD97 are computed. The map-derived TWD97 coordinates of the control points are used to obtain coordinates of land boundaries, which are then compared with the GPS-measured coordinates. This comparison helps to assess the accuracy of coordinate transformation for the digitized maps.